The application relates generally to substrate processing methods and particularly to process sequences which increase the density of features on the substrate.
Shrinking integrated circuits (ICs) may result in improved performance, increased capacity and/or reduced cost. Each device shrink requires more sophisticated techniques to form the features. Photolithography is commonly used to pattern features on a substrate. An exemplary feature is a line of a material which may be a metal, semiconductor or insulator. The linewidth is the width of the line and the spacing is the distance between adjacent lines. Pitch is defined as the distance between a same point on two neighboring lines. The pitch is equal to the sum of the linewidth and the spacing. Due to various factors including the radiation wavelength, photolithography techniques have a minimum pitch below which a particular photolithographic technique may not reliably form features. Clearly, the minimum pitch of any given photolithographic technique can limit feature size reduction.
Self-aligned double patterning (SADP) is one method for extending the capabilities of photolithographic techniques beyond their supposed minimum pitch. Such a method is illustrated in FIGS. 1A-G. With reference to FIG. 1A, patterned features 111 are formed from sacrificial structural material above a substrate 100 using standard photo-lithography and etching techniques. The patterned features 111 are referred to as placeholders, mandrels or cores and have linewidths and/or spacings near the optical resolution of a photolithography system using a high-resolution photomask. As shown in FIG. 1B, a conformal layer 130 of hard mask material is subsequently deposited over cores 111. Hard mask spacers or ribs 131 are then formed on the sides of cores 111 by preferentially etching the hard mask material from the horizontal surfaces with an anisotropic spacer etch. The resulting structure is shown in FIG. 1C. Cores 111 may then be removed, leaving behind hard mask spacers 131 (FIG. 1D). At this point hard mask spacers 131 may be used as an etch mask for patterning the substrate and subsequently removed in a positive tone process flow. Alternatively, in a negative tone process, regions between the spacers are filled with material (140 in FIG. 1E), the filler material is etched back (141 in FIG. 1F) and used as a mask after spacers 131 are removed (FIG. 1G). With either positive or negative tone process flows, the density of features is twice that of the photo-lithographically patterned features. In the figures, the pitch of hard mask spacers or ribs 131 is half the pitch of patterned features 111. The process flows outlined above decrease the pitch along one dimension.